This is a Spike's Tactical Stripped Lower Receiver known as the STLS019 chambered in 223 Remington, model STLS019-CE.
Spike's lowers are made to the highest standards. If you are planning a build or just putting lowers away for a rainy day" you can't go wrong with Spike's lower receivers.
Features:
Multi Caliber
Hard Coat Anodized Finish
Lower Receiver